Data reader and methods for imaging targets subject to specular reflection

ABSTRACT

A data reader such as for example an imaging reader with a CCD or CMOS imager or the like, having multiple images of a target item illuminated or acquired from different directions in which the image signals are combined into a complete image of the item or selected portions of the item being read such that specular reflection (over-saturated regions of the sensor array) are minimized or eliminated. In one example data reader configuration, multiple illumination sources such as first and second rows of light emitting diodes (LED&#39;s) are aimed at the item being scanned from different directions. The illumination sources are alternately pulsed and return signals are collected at one or more sensor arrays. A selected non-saturated return signal from one of the illumination sources, or selected non-saturated portions of return signal from both of the illumination sources are processed to generate a complete non-saturated image of the target. In one preferred processing scheme, assuming that each of the LED&#39;s is capable of illuminating the entire target (e.g. a barcode), a pixel-by-pixel minimum is taken of the two images thereby producing an image with specular reflection minimized or nearly eliminated.

BACKGROUND

The field of this disclosure relates to imaging and collection devicesand in particular to methods and devices for illumination, collectionand imaging for optical code reading and other data and image capturedevices.

Image capture and other data reading devices are used to read opticalcodes, acquire data, and capture a variety of images. One common dataacquisition device is an optical code reader. Optical codes typicallycomprise a pattern of dark elements and light spaces. There are varioustypes of optical codes, including 1-D codes (such as UPC and EAN/JANbarcodes) and 2-D codes (such as PDF-417 and Maxicode). For convenience,some embodiments are described herein with reference to capture of 1-Dbarcodes. However, the embodiments may also be useful for other opticalcodes and symbols as well as other images such as fingerprint capture,and nothing herein should be construed as limiting this disclosure tooptical codes or particular types of codes.

One type of data reader is an imaging reader that employs an imagingdevice or sensor array, such as a CCD (charge coupled device) or CMOSdevice. Imaging readers can be configured to read both 1-D and 2-Doptical codes, as well as other types of optical codes or symbols andimages of other items. When an imaging reader is used to read an opticalcode, an image of the optical code or portion thereof is focused onto adetector array. Though some imaging readers are capable of using ambientlight illumination, an imaging reader typically utilizes a light sourceto illuminate the item being scanned, to provide the required signalresponse in the imaging device.

The present inventors have recognized that light from high-intensityillumination can reflect off certain surfaces such as metal canscreating a specular reflection of too high an intensity therebyoversaturating the sensor array resulting in ineffective detection.Thus, the present inventors have identified a need for compensating forthis reflection condition to enhance data reader performance.

SUMMARY

Methods and devices are disclosed for improving reading of optical codesor other items being imaged, particularly where the read surface isreflective such that illumination tends to oversaturate the sensor arrayor portions thereof.

In a preferred configuration, the data reader comprises an imagingreader, such as a CCD or CMOS imager, having multiple images of a targetitem illuminated or acquired from different directions in which thesignals are combined into a complete image of the item or selectedportions of the item being read such that specular reflection(over-saturated regions of the sensor array) are minimized oreliminated. In one example data reader configuration, multipleillumination sources such as first and second rows of light emittingdiodes (LED's) are aimed at the item being scanned from differentdirections. The illumination sources are alternately pulsed and returnsignals are collected at one or more sensor arrays. A selectednon-saturated return signal from one of the illumination sources, orselected non-saturated portions of return signal from both of theillumination sources are processed to generate a complete non-saturatedimage of the target. In one preferred processing scheme, assuming thateach of the LED's is capable of illuminating the entire target (e.g. abarcode), a pixel-by-pixel minimum is taken of the two images therebyproducing an image with specular reflection minimized or nearlyeliminated.

Additional aspects and advantages will be apparent from the followingdetailed description of preferred embodiments, which proceeds withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 diagrammatic view of a data reader according to a preferredembodiment.

FIG. 2 is a schematic front view of a layout for a data reader as inFIG. 1.

FIG. 3 is a schematic side view of a layout for a data reader as inFIGS. 1-2.

FIG. 4 is an image of a barcode on beverage can taken by the data readeras in FIGS. 2-3 with the barcode illuminated by both top and bottom rowsof illumination sources.

FIG. 5 is an image of a barcode on a beverage can taken by the datareader as in FIGS. 2-3 with the barcode illuminated by only the top rowof illumination sources.

FIG. 6 is an image of the barcode on the beverage can taken by the datareader as in FIGS. 2-3 with the barcode illuminated by only the bottomrow of illumination sources.

FIG. 7 is an image of the barcode on the beverage can combining theimages of FIGS. 5 and 6 as processed by a pixel-by-pixel minimum scheme.

FIG. 8 is an image of a barcode on a reflective candy wrapper taken bythe data reader as in FIGS. 2-3 with the barcode illuminated by only thetop row of illumination sources.

FIG. 9 is an image of the barcode on the candy wrapper taken by the datareader as in FIGS. 2-3 with the barcode illuminated by only the bottomrow of illumination sources.

FIG. 10 is an image of the barcode on the candy wrapper combining theimages of FIGS. 8 and 9 as processed by a pixel-by-pixel minimum scheme.

FIG. 11 diagrammatic view of a data reader according to anotherembodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout the specification, reference to “one embodiment,” or “anembodiment,” or “some embodiments” means that a particular describedfeature, structure, or characteristic is included in at least oneembodiment. Thus appearances of the phrases “in one embodiment,” “in anembodiment,” or “in some embodiments” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the described features, structures, characteristics, andmethods may be combined in any suitable manner in one or moreembodiments. In view of the disclosure herein, those skilled in the artwill recognize that the various embodiments can be practiced without oneor more of the specific details or with other methods, components,materials, or the like. In other instances, well-known structures,materials, or operations are not shown or not described in detail toavoid obscuring aspects of the embodiments.

Preferred embodiments will now be described with reference to thedrawings. To facilitate description, any reference numeral representingan element in one figure will represent the same element in any otherfigure.

Methods and devices according to the embodiments described areparticularly useful for presentation scanners utilizing imagingtechnology. For conciseness of description, the detector arrays aredescribed as CCD arrays, but other suitable detectors may be implementedsuch as CMOS.

FIG. 1 is a diagrammatic view of a data reader 10 in accordance with afirst embodiment. The data reader 10 is schematically depicted as apresentation scanner suitable for reading optical codes, symbols orother items. Scanner 10 includes a head portion 12 attached to a handleportion 14, with the handle portion 14 mounted onto a base 16. Scanner10 may operate as a presentation scanner being self-supported on ahorizontal surface or mountable to such a surface or a wall. The reader10 is self-supporting on the base 16 usable in a hands free mode. Thereader 10 may also be grasped about the handle and operated in ahand-held or portable mode with scanning activated by actuation of thetrigger 18. The reader may be operable in multiple modes or multipleread patterns as described in U.S. Pat. No. 6,575,368, herebyincorporated herein by reference. A bar code on an object such asbeverage can 30 may be read by presenting the bar code into the scannerread region in front of the window 13. The data reader 10 has two rowsof illumination sources in the top row 22 comprised in this embodimentof four LEDs arranged in a line above the detector 20. Similarly asecond row of LEDs 24 is located in a similar position below thedetector 20. In a preferred configuration, the first and second rows ofLEDs 22, 24 are aimed into the scan region such that each row of LEDseach completely illuminates the bar code on the object 30 beingpresented to the data reader 10.

FIGS. 2-3 schematically illustrate front and side views of the datareader of FIG. 1. FIG. 2 illustrates the top row of LEDs 22 beingcomprised of four LEDs generally arranged in a line above the focusinglens 21. The focusing lens 21 collects light reflecting off the object30 and focuses the return signal light onto the detector 20. The bottomrow of LEDs 24 also comprises four LEDs generally arranged in a linebelow the lens 21. Other numbers of LEDs or arrangements may beutilized. In a preferred configuration, the top and bottom illuminationsources 22, 24 are offset but directed toward the item being scanned toilluminate the same scan region or substantially overlapping scanregions.

When the item being read has a highly reflective surface such as the barcode on the side of the aluminum beverage can 30, the light from theillumination sources 22, 24 efficiently reflects off the metal surfaceand tends to oversaturate the detector 20 of the imaging system.

FIG. 4 illustrates an image of a bar code on the beverage can as takenby the data reader of FIGS. 2-3 with the bar code illuminated by boththe top and bottom rows 22, 24. As shown in FIG. 4, the highlyreflective metal surface of the can 30 efficiently reflects light fromthe illumination sources and oversaturates the detector resulting inregions 34, 36 of the image not being effectively read. The diffractionpattern caused by the microscopic vertical grooves in the can's surfacecaused by the forming process spreads horizontally in the image,preventing successful processing of the barcode image even in theregions to the left and right of the primary specular reflection.However, since the rows of LEDs 22, 24 are offset in opposite directionsabove and below the lens 21, the light from the two illumination sources22, 24 are directed along different incoming angles to the surface ofthe bar code 32. FIG. 5 illustrates an image as detected at the detector20 where only the top row of LEDs 22 is illuminated. As viewed in thefigure only a top portion of the bar code label has an oversaturatedregion 34. In FIG. 6, images taken of the bar code 32 only illuminatedby the bottom row of LEDs 24. FIG. 6 illustrates that only a bottomportion of the image experiences an oversaturation region 36.

Examination of the images of FIGS. 5 and 6 reveals that the bottomportion of the bar code 32 in the image of FIG. 5 is relatively clear ofoversaturation regions and the top portion of the bar code 32 in theimage of FIG. 6 is relatively free of oversaturation regions at the topof the bar code. Thus by sequentially or alternatingly illuminating thebar code first with the top LED array 22 and acquiring the image of FIG.5 and then subsequently illuminating the bar code only with the bottomLED array 24 and acquiring the image of the bar code of FIG. 6, thesystem may process the two images together to create a combined image ofthe bar code 32 as shown in FIG. 7.

In a preferred configuration where each row of LEDs 22, 24 is capable ofilluminating the entire target (the bar code in this case) one preferredmethod is using a pixel-by-pixel minimum of the two images. In otherwords data from the two image scans are analyzed comparing the relativeintensities of the pixel from the first image to the intensity of thepixel at the same spatial location in the second image, the algorithmselecting the image with the lower intensity thereby discarding a pixelthat is experiencing specular reflection or otherwise oversaturating thedetector. FIG. 7 illustrates a combination of the images of FIGS. 6 and7 utilizing the pixel-by-pixel minimum selection criteria.

Once the image is acquired with the specular reflection beingeliminated, the image may be processed to read the data captured(example the bar code) using a suitable methodology such as a virtualscan line system as disclosed in U.S. Pat. No. 5,635,699 herebyincorporated by reference.

Attention should be given to the choice of separation of illuminationsources as such separation can improve system performance. In oneconfiguration where the bar code is on the side of a beverage can, wherethe beverage can is being read in an orientation relative to the datareader as illustrated in FIG. 1 the curvature of the can would tend toreduce the separation of any sequential illumination where the rows ofLEDs were arranged to the left and right of the sensor (as if the datareader 10 of FIG. 1 were rotated 90 degrees relative to the can 30). Inaddition the diffraction pattern caused by surface irregularities in thecan would cause horizontal stripes that would not be readily eliminatedby the processing method. Thus for beverage cans, the illuminationorientations are preferably above and below the sensor 20 facing avertically oriented can.

For other types of highly reflective labels the orientation of theillumination sources may not be critical or may have other orientationpreferences. For example coded Mylar wrappers, such as candy barwrappers, have high specular reflection. Since the wrappers aretypically crinkled, there may be specular reflections in several placeson the wrapper due to illumination in various directions. The sequentialillumination may be from any two distinct orientations to achieve adesired effect. Objects with a flat surface, such as plate glass, mayalso have sequential illumination from any direction. FIGS. 8-9illustrates an illumination method as applied to a bar code 40 on acandy wrapper. FIG. 8 illustrates the bar code 40 being illuminatedsolely by the top row of LEDs 22 whereby the image experiences three (ormore) oversaturation regions 42, 43, 44. FIG. 9 illustrates an image ofthe bar code 40 as illuminated solely by the bottom row of LEDs 22, theimage experiencing oversaturation regions 46, 48. In the two images ofFIGS. 8 and 9 via the pixel-by-pixel minimum processing method aspreviously described generating an image of the bar code 40 as in FIG.10 whereby the specular reflection is substantially removed.

To achieve a desirably rapid sweep speed, it is preferred that the twoimages be taken as close together in time as practical. One method oftaking the pixel minimum of two frames may assume that there is nomovement between the frames. Since the exposure time of an LED imagerdesigned for moving targets is quite small, the time delay from frame toframe is dominated by the readout time of the images. To reduce thereadout time, it may be advantageous to reduce the area of the image tobe read out to contain only the region of interest. For example, in FIG.3, a narrow vertical stripe of pixels may be all that is needed to beread since the bar code is oriented in such a way that a vertical scanline would cross all of the bars and spaces of the bar code. By reducingthe number of pixels to be read, the readout time is greatly reduced,thereby reducing the time delay between frames and more ideally meetingthe assumption of no motion between the frames.

One way of processing these portions of the images efficiently may be bystoring the first frame, or a subset of the frame according to a virtualscan line processing method such as disclosed in U.S. Pat. No. 5,635,699(already incorporated by reference) in memory. As the second frame isread out of the imager, each pixel is compared to the pixel stored fromthe previous frame. If the new pixel is smaller, it is stored in thesame location in place of the pixel of the previous frame. Otherwise thepixel of the previous frame is left in memory. This process uses asimple yes/no decision when choosing each pixel as between two images.

Alternate processing schemes may be utilized. In theory, the signallevel at a particular pixel location has a preferred intensity range.When the sensor has oversaturated pixels or regions, the intensity istoo high indicative of specular reflection. In alternate process, theintensities of the pixels from the first frame (or a subset of the frameaccording to a virtual scan line processing method) are stored, inmemory. As the second frame is read out of the imager, the pixels of thefirst frame and the pixel from the second frame are compared to apreferred intensity range and the lower intensity pixel is chosen unlessthat pixel has too low an intensity and the upper intensity pixel is notabove a maximum intensity.

The data reader 10 preferably comprises an imaging reader having asuitable detector array 20 such as a complementary metal oxidesemiconductor (CMOS) imager. The imager is coupled to a processor (showndiagrammatically as element 15 in FIG. 3) for reading optical codes andother symbols or imaged items such as a fingerprint. A CMOS imager has afield of view inclusive of scan zone within which a target item may bepresented for imaging. A CMOS imager may comprise an active-pixelimaging sensor with a global shutter (simultaneous total-pixel exposuresystem—also referred to as “frame shutter exposure”) and good nearinfrared (NIR) sensitivity, such as a model MT9V022 sensor sold byMicron Technology, Inc. of Boise, Id., USA. In some embodiments,multiple CMOS imagers may be employed for reading items in multipledifferent read volumes, of which some volumes may overlap.

The processor 15 may comprise any suitable digital processor, such as alow-power DSP core or ARM core processor. In preferred embodiments,processor 15 comprises an OMAP processor sold by Texas Instruments ofDallas, Tex., USA or an i.MX1 series processor (such as the MC9328MX1processor) sold by Freescale Semiconductor, Inc. of Austin, Tex., USA.Alternately, multiple processors or sub-processors or other types ofprocessor electronics such as comparators or other specific functioncircuits may be used alone or in combination. For the purposes of thisdescription, the term processor is meant to any of these combinations.

In other embodiments (not shown), data reader 10 may comprise othertypes of data readers, such as a moving spot laser scanner, for example.Data reader 10 may also comprise a dual-mode scanner, such as the kinddescribed in U.S. Pat. No. 6,575,368, already incorporated by reference.

The illumination sources preferably comprises a collection of infraredor visible spectrum LEDs, but may alternatively comprise another kind oflight source, such as a lamp or laser diode, for example. An infraredsource preferably emits diffuse infrared radiation at a near-infraredwavelength of about 850 nm, although non diffuse sources and sources ofother wavelengths may also be used. The illumination sources may becoupled to and controlled by the processor 15, or may be remotelymounted and powered. A power supply circuit shown schematically aselement 29 is preferably provided for energizing the LEDs. The top andbottom LED arrays 22, 24 are preferably both pulsed in alternatingsuccession or at suitable rates and/or times.

In an alternate system, the configuration of the sensor and illuminationsources are reversed. FIG. 11 illustrates an alternate data reader 50comprised of a scan head 52 with single row of LEDs 64 located betweenfirst and second sensor arrays 60, 62. The light source 64 is pulsed anddirected out through window 53 and reflected light from the same pulseis detected by the first and second sensor arrays 60, 62. The angle ofreflection from the light source to each of the sensors will bedifferent. Thus where an image region sensed by the first sensor array60 experiences specular reflection, the corresponding image regionsensed by the second sensor 62 array may not. Corresponding pixels ofthe two images (or a subset thereof according to a virtual scan lineprocessing method) are compared and the pixel with the lower intensityis selected. The resulting pixel image is stored or sent forprocessing/decoding. One advantage of this system may be that bothsensor arrays record an image at the same instant, so there is noconcern about product movement between captured images. However, in ageneral case, processing will likely be required in order to resolve theparallax issue between the sensors, i.e., determine which pixels in thefirst sensor are imaging the same location as pixels in the secondsensor. In various applications, one variable, the motion betweenframes, or the parallax between imagers may be controlled in such afashion so as to prefer the use of one embodiment over another.

Alternately, the systems may be combined. The LEDs 64 may be controlledby a controller 69 to illuminate at different times. For example, leftside LEDs 64 a, 64 b may illuminate first with the image captured by oneor both sensors 60, 62 and then right side LEDs 64 c, 64 d mayilluminate second with the image captured by one or both sensors 60, 62.

Thus systems and methods for data reading and image capture that reducespecular reflection or compensate for signal oversaturation have beenshown and described. It is nevertheless intended that modifications tothe disclosed systems and methods may be made by those skilled in theart without departing from the underlying principles of set forthherein. The scope of the present invention should, therefore, bedetermined only by the following claims.

1. A method of data reading comprising the steps of: passing an item tobe read into a scan region; offsetting a first illumination source froma second illumination source; at a first point in time, illuminating afirst portion of the scan region with the first illumination source andacquiring a first image of the item; at a second point in timesubsequent to the first point in time, illuminating a second portion ofthe scan region with the second illumination source and acquiring asecond image of the item, the first portion and the second portion beingat least partly overlapping; comparing a discrete portion of the firstimage to a corresponding discrete portion of the second image andselecting that discrete portion having a lower intensity; repeating saidstep of comparing for each of the discrete portions of the first andsecond images; assembling a combined image of the item from the selecteddiscrete portions; processing the combined image.
 2. A method accordingto claim 1 wherein the first illumination source is a row of LEDs.
 3. Amethod according to claim 1 further comprising a sensor array positionedbetween the first illumination source and the second illuminationsource.
 4. A method according to claim 3 wherein the first illuminationsource is a row of LEDs positioned above sensor array and the secondillumination source is a row of LEDs positioned below the sensor array.5. A method according to claim 1 wherein the step of comparing comprisescomparing incoming signal of the second image on a pixel-by-pixel basisto the pixels of the first image at corresponding spatial locations. 6.A system for data reading of an item within a scan region, comprising: afirst illumination source that directs a first illumination onto asurface of the item in the scan region from a first direction; a secondillumination source that directs a second illumination onto the surfaceof the item in the scan region from a second direction different thanfirst direction; a controller for alternately activating the firstillumination source and the second illumination source; a sensor fordetecting a first return signal from the first illumination reflectingfrom the item and for detecting a second return signal from the secondillumination reflecting from the item; a processor for comparingrelative intensities of corresponding discrete portions of the first andsecond return signals, choosing a selected one of the discrete portionshaving a lower intensity, and combining the signals into a completeimage of the item or selected portions of the item being read.
 7. Asystem according to claim 6 wherein the system comprises a presentationscanner.
 8. A system according to claim 6 wherein the complete image ofthe item or selected portions of the item being read is a plurality ofvirtual scan lines representative of the image within the scan region.9. A system according claim 6 wherein the discrete portion beingcompared comprises a specific pixel location on the sensor, theprocessor performing a pixel-by-pixel comparison of the first and secondreturn signals and choosing the return signal for each specific pixellocation having a lower intensity.
 10. A system according claim 6wherein the processor combines the signals by selecting the discreteportions having an intensity in a preferred intensity range.
 11. Asystem for data reading of an item within a scan region, comprising: afirst illumination source that directs a first illumination onto asurface of the item in the scan region; a first sensor array arrangedoffset from the first illumination source in a first direction fordetecting a first return signal from the first illumination reflectingfrom the item; a second sensor array arranged offset from the firstillumination source in a second direction for detecting a second returnsignal from the first illumination reflecting from the item; processorfor comparing relative intensities of discrete portions of the first andsecond return signals and combining the signals into a complete image ofthe item or selected portions of the item being read, wherein theprocessor combines the return signals by choosing a selected one of thediscrete portions of the first and second return signals having a lowerintensity.
 12. A system according claim 11 wherein the processor choosesa selected one of the first and second discrete portions depending onthe comparing.
 13. A system according claim 11 wherein the processorcombines the return signals by selecting the discrete portions having anintensity in a preferred intensity range.
 14. A system for data readingof an item within a scan region, comprising: a first illumination sourcethat directs a first illumination onto a surface of the item in the scanregion; a first sensor array arranged offset from the first illuminationsource in a first direction for detecting a first return signal from thefirst illumination reflecting from the item; a second sensor arrayarranged offset from the first illumination source in a second directionfor detecting a second return signal from the first illuminationreflecting from the item; processor for comparing relative intensitiesof discrete portions of the first and second return signals andcombining the signals into a complete image of the item or selectedportions of the item being read, wherein the discrete portion beingcompared comprises a specific pixel location on the sensor array, theprocessor performing a pixel-by-pixel comparison of the first and secondreturn signals and choosing the return signal for each specific pixellocation having a lower intensity.
 15. A method of data readingcomprising the steps of: offsetting a first image array from a secondimage array; illuminating a first portion of a scan region with a firstillumination source and acquiring a first image of an item with thefirst sensor array from a first angular direction and acquiring a secondimage of the item with the second sensor array from a second angulardirection different than the first angular direction; comparing adiscrete portion of the first image to a corresponding discrete portionof the second image and selecting that discrete portion being lesssubjected to specular reflection; repeating said steps of illuminatingand comparing for each of the discrete portions of the first and secondimages of the item; assembling a combined image of the item from theselected discrete portions; processing the combined image, wherein thestep of comparing comprises performing a pixel-by-pixel comparisonbetween the first and second images.
 16. A method according to claim 15wherein the step of selecting that discrete portion being less subjectedto specular reflection comprises choosing the discrete portion having asignal of lower intensity.
 17. A method according to claim 15 whereinthe step of selecting that discrete portion being less subjected tospecular reflection comprises selecting the discrete portion having asignal of an intensity in a preferred intensity range.